A Nearly Planar Stannene with a Reactive Tin-Carbon Double Bond

Bis(2,4,6‐triisopropylphenyl)‐2,7‐di‐tert‐butylfluorenylidenestannane, Tip2Sn=CR2, an isolable stannene that displays a deep‐purple colour, was synthesized by dehydrofluorination of the corresponding fluorostannane by tert‐butyllithium. It exhibits the shortest Sn=C distance [2.003(5) Å] and the slightest twisting around this unsaturation (10°) among the known stannenes. Its reaction with benzaldehyde according to a [2+2] cycloaddition and that with α‐ethylenic aldehydes and ketones such as crotonaldehyde and methyl vinyl ketone by a [2+4] cycloaddition proceeded in near‐quantitative yield. With acetone, an ene reaction occurred. The four‐membered ring 1,2‐oxastannacyclobutane obtained with benzaldehyde underwent a ring expansion with a second molecule of benzaldehyde to afford the six‐membered ring dioxastannacyclohexane.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) The isolable bis(2,4,6‐triisopropylphenyl)‐2,7‐di‐tert‐butylfluorenylidene stannane, Tip2Sn=CR2, exhibits the shortest Sn=C distance [2.003(5) Å] and the slightest twisting (10°) among stannenes. It undergoes [2+2] cycloaddition with benzaldehyde, [2+4] cycloadditions with α‐ethylenic aldehydes and ketones and an ene reaction with acetone.